I think there's also this naive notion among people who haven't thought it through and/or aren't very familiar with manufacturing processes and the like that if you have the "blueprints" for something, it's straightforward to cart them down to a general-purpose factory and build the thing. After all, if we built it once, how hard can it be to build it again? And even some who may understand that it's not quite that simple still don't necessarily appreciate just how complex and intertwined the relationships are between suppliers, tooling, processes, experts in very specific and narrow domains, and so forth are when building any sort of complex machine.
Yeah, even with the exact blueprints, you couldn't just make a new Saturn V. The tools that made those parts probably don't exist any more, and the properties of metal under stress depend on a bunch of weird circumstances, like exactly how you cooled down the molten metal.
And even if you wrote that down and had all that equipment, the people who actually operated the things are retired or dead. Are you going to operate it the same way they did?
Does your incoming metal to your smelter have all the same properties as it did in the 1960s?
(I'm not a metallurgist, apologies to those who are.)
Yep, we haven't lost the tech, just the in-house skills. Each Saturn V engine had an absolutely insane number of extremely fine welds by master welders. Welding is an art form, and we definitely don't have the same number of welders we used to.
That said, we could potentially replace some of that with new fab techniques. But we probably couldn't do it the same way we did.
